The present invention relates to a method of forming a CVD-Ti film used as, e.g., a contact metal or adhesion, in a semiconductor device and, more particularly, to a CVD-Ti film forming method of forming a Ti film as a barrier layer in a hole of an insulating film which covers a silicon substrate and in which the hole is formed.
In the manufacture of a semiconductor device, to meet recent demands for higher density and higher integration degree, the circuit arrangement more often has a multilayer interconnection structure. In order to make electrical connection between a lower semiconductor device and an upper interconnection layer that are insulated from each other by an insulating film, e.g., an SiO.sub.2 film, interposed between them, a technique that forms a buried portion in a hole, e.g., a contact hole or a via hole, formed in the insulating layer by CVD, thus achieving electrical connection between the upper and lower layers becomes significant.
In the above technique, to fill the contact hole or via hole, generally, Al (aluminum) or W (tungsten), or an alloy containing Al or W as a major component is used. When such a metal or alloy comes into direct contact with the lower Si (silicon) substrate or the Si layer, the metals may undesirably form an alloy in the boundary portion of the lower Si substrate or Si layer due to the absorbing effect of Si or the like. The alloy formed in this manner has a large electric resistance. Such alloying is not preferable in terms of power savings and higher operation speed that are recently demanded of the device.
When W or a W-alloy is used as a buried layer of a contact hole, WF.sub.6 gas used in forming the buried layer enters the Si substrate to degrade the electrical characteristics and the like.
In order to prevent these inconveniences, before formation of a buried layer in a contact hole or via hole, a barrier layer is formed on the inner surface of the hole in advance, and then the buried layer is formed on the barrier layer. As this barrier layer, a layer formed by a Ti (Titanium) film or a two-laminated structure layer consisting of a Ti film and a TiN (titanium nitride) film is generally used.
This barrier layer is commonly formed by physical vapor deposition (PVD). As micropatterning and higher integration of the devices are particularly required recently and the design rule becomes particularly strict, the line width and the hole aperture diameter continue to decrease to result in an increase in aspect ratio. Along with this, the electrical resistance of the PVD film increases, making it difficult to meet the above demands.
For this reason, the Ti film and TiN film that construct the barrier layer are formed by chemical vapor deposition (CVD) which can form a higher-quality film. When forming the Ti film by CVD, TiCl.sub.4 (titanium tetrachloride) and H.sub.2 (hydrogen) are used as the reaction gases. When forming the TiN film, TiCl.sub.4 and NH.sub.3 (ammonia) or MMH (monomethyl hydrazine) are used as the reaction gases.
In recent years, semiconductor devices continue to shrink in feature size and the aspect ratio of a contact hole or via hole formed in an SiO.sub.x (e.g., SiO.sub.2) film continues to increase. Therefore, with the conventional TiCl.sub.4 and H.sub.2 gas systems, it is difficult to form a CVD-Ti film in the hole portion with a good step coverage equal to or higher than 100%.